1. Field of the Invention
This invention relates to a fiber bond type ceramic material, and, more particularly, to a method for the production of a ceramic material of the type having fibers three dimensionally bonded thereto, and engine parts formed of the material.
2. Description of Related Art
A Si--Ti--C--O fiber bond type ceramic material (sold under the trademark of "Tyrannohex [transliteration]") produced by pressing surface-oxidized Si--M--C--O fibers (sold under the trademark of "Tyranno [transliteration]Fibers") has been published ("Microstructure and Characteristics of Si--Ti--C--O Fiber-bond Type Ceramic Material," Jul. 18, 1995, the 76th Ceramic Material Division Committee of Japan Material Society, for example) and has been the subject of patents (Japanese Patent No. 2,579,854, titled "Inorganic fiber sinter and method for production thereof").
The Tyranno fibers (Si--M--C--O-fibers, M means metal) are inorganic fibers of Si--M--C--O synthesized by melt spinning polymetalocarbosilane, then infusibilizing the produced threads, and firing the set threads. The Tyrannohex (Si--M--C--O fiber-bond type ceramic) material is produced by heat-treating the Tyranno fibers in the air and obtaining oxidized Tyranno fibers having an oxide layer on the surface thereof, preparing unidirectional prepreg sheets from the fibers, superimposing the sheets uniformly in alignment, and compressing the superimposing sheets with a hot press machine at an elevated temperature.
In the Tyrannohex material constructed as described above, a matrix layer has been formed by hot-pressing oxided fibers and the gaps between the adjacent fibers are uniformly filled with the oxide formerly existent on the surface of the raw material fibers and consequently allowed to form a dense texture veritably destitute of pores. Further, since the Tyranno fibers themselves possess high mechanical properties and excellent heat-resistance and oxidation-resistance, the Tyrannohex material likewise excels in mechanical strength and in heat-resistance and oxidation-resistance.
Machining the Tyrannohex material to manufacture engine parts by making the best use of such characteristics of the Tyrannohex (fiber-bond type ceramic) material has been desired. When some turbine parts as, for example, rotor blades and stationary vanes, shrouds, combustors, the afterburner flaps, and split-structure liners are produced by machining the Tyrannohex material, the parts have a heightened heat-resistant strength (not lower than 1400.degree. C.) and a decreased weight (specific gravity about 2.6) as compared with equivalent turbine parts made of the conventional heat-resistant metal (tolerable temperature about 1000.degree. C. and specific gravity about 8).
The Tyrannohex material, however, has the problem of readily sustaining tears when it is cut in fabricating a turbine part. When a unidirectional Tyrannohex material is clamped in a vice and a cut is made in the material in a direction perpendicular to the fibers therein. For example, the complex stress originating in the friction resistance generated by the rotational of a grindstone and the rotation moment generated during the course of cutting under the weight of the grindstone possibly acts on the boundaries of the fibers and causes separation of the fibers at the interfaces.
When then the Tyranno fibers are two-dimensionally woven and they are superposed to produce a Tyrannohex material for the purpose of overcoming the problem mentioned above, the Tyrannohex material has the further problem of readily sustaining separation of superposed weaves at the interfaces when the material is subjected to machining.
Further, attempts to produce a Tyrannohex material by orthogonally weaving Tyranno fibers in such a construction as contains fibers parallel to the direction of compression for the purpose of precluding this separation, suffer from the disadvantage that the raw material fibers, during the course of hot-press fabrication, form kinks and incur a heavy loss of strength, have voids produced readily therein, and prevent formation of a dense matrix layer, with the result that the produced Tyrannohex material will have an unduly low volumetric fiber content and will exhibit serious degradation of heat-resistant strength.